U.S. patent number 10,864,460 [Application Number 15/515,960] was granted by the patent office on 2020-12-15 for graphene-based inorganic-organic hybrid materials and separation of racemic mixtures.
This patent grant is currently assigned to UNM Rainforest Innovations. The grantee listed for this patent is Plamen B Atanassov, Liliya V Frolova, Nikolai Kalugin, Alexey Serov. Invention is credited to Plamen B Atanassov, Liliya V Frolova, Nikolai Kalugin, Alexey Serov.
United States Patent |
10,864,460 |
Serov , et al. |
December 15, 2020 |
Graphene-based inorganic-organic hybrid materials and separation of
racemic mixtures
Abstract
A variety of inorganic-organic hybrid materials and various
methods for preparing and using the same are described. The hybrid
materials are graphene or graphitic materials populated with
organic molecules and may have a variety of surface defects, pits
or three-dimensional architecture, thereby increasing the surface
area of the material. The hybrid materials may take the form of
three dimensional graphene nanosheets (3D GNS). If the organic
molecules are enantiospecific molecules, the hybrid materials can
be used for chiral separation of racemic mixtures.
Inventors: |
Serov; Alexey (Albuquerque,
NM), Atanassov; Plamen B (Santa Fe, NM), Kalugin;
Nikolai (Albuquerque, NM), Frolova; Liliya V (Socorro,
NM) |
Applicant: |
Name |
City |
State |
Country |
Type |
Serov; Alexey
Atanassov; Plamen B
Kalugin; Nikolai
Frolova; Liliya V |
Albuquerque
Santa Fe
Albuquerque
Socorro |
NM
NM
NM
NM |
US
US
US
US |
|
|
Assignee: |
UNM Rainforest Innovations
(Albuquerque, NM)
|
Family
ID: |
1000005242511 |
Appl.
No.: |
15/515,960 |
Filed: |
September 30, 2015 |
PCT
Filed: |
September 30, 2015 |
PCT No.: |
PCT/US2015/053074 |
371(c)(1),(2),(4) Date: |
March 30, 2017 |
PCT
Pub. No.: |
WO2016/054129 |
PCT
Pub. Date: |
April 07, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170253489 A1 |
Sep 7, 2017 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
62057313 |
Sep 30, 2014 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
20/286 (20130101); B01J 20/3251 (20130101); B01D
15/08 (20130101); B01J 20/28014 (20130101); B01J
20/205 (20130101); C01B 32/196 (20170801); G01N
30/62 (20130101); C01B 32/21 (20170801); G01N
30/14 (20130101); G01N 30/02 (20130101); C07C
51/47 (20130101); C01B 32/182 (20170801); B01J
20/3064 (20130101); B01J 20/22 (20130101); C07D
207/08 (20130101); C07C 51/47 (20130101); C07C
57/30 (20130101); C07B 2200/09 (20130101); G01N
2030/146 (20130101); G01N 2030/623 (20130101); G01N
2030/143 (20130101); G01N 2030/027 (20130101); G01N
2030/621 (20130101) |
Current International
Class: |
B01D
15/08 (20060101); G01N 30/62 (20060101); B01J
20/22 (20060101); C01B 32/21 (20170101); B01J
20/286 (20060101); B01J 20/30 (20060101); B01J
20/32 (20060101); C07D 207/08 (20060101); C01B
32/196 (20170101); C07C 51/47 (20060101); C01B
32/182 (20170101); G01N 30/02 (20060101); B01J
20/20 (20060101); G01N 30/14 (20060101); B01J
20/28 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Jiang et al. Design of advanced porous graphene materials: from
graphene nanomesh to 3D architectures. Nanoscale, 2014, 6,
1922-1945. (Year: 2014). cited by examiner .
Gubitz et al. Resolution of the enantiomers of barbiturates on a
new chiral amino alcohol phase by CLEC. Quimica Analitica (1993)
12:45-47. (Year: 1993). cited by examiner .
Hauser et al. Functionalized graphene as a gatekeeper for chiral
molecules: An alternative concept for chiral separation. Angew.
Chem. Int. Ed. (2014) 53, 9957-9960. (Year: 2014). cited by
examiner .
Huh et al. UV/Ozone-oxidized large-scale graphene platform with
large chemical enhancement in surface-enhanced raman scattering.
ACS Nano, vol. 5, No. 12 (2011) 9799-9806. (Year: 2011). cited by
examiner .
Surface-modified threedimensional graphene nanosheets as a
stationary phase for chromatographic separation of chiral drugs,
Scientific Reports (2018) 8:14747. cited by applicant.
|
Primary Examiner: McDonald; Katherine Zalasky
Attorney, Agent or Firm: Gonzales Patent Services Gonzales;
Ellen M.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The following application claims benefit of U.S. Provisional
Application No. 62/057,313, filed Sep. 30, 2014, which is hereby
incorporated by reference in its entirety.
Claims
What is claimed is:
1. An inorganic-organic hybrid material comprising a
non-contiguous, three-dimensional graphene material comprising at
least two layers of carbon atoms and comprising a plurality of
voids wherein the graphene material is populated with organic
molecules.
2. The inorganic-organic hybrid material of claim 1 wherein the
organic molecule is an enantioselective molecule.
3. The inorganic-organic hybrid material of claim 2 wherein the
enantioselective molecule is (S)-(+)-2-pyrrolidinemethanol.
4. The inorganic-organic hybrid material of claim 1, wherein the
three-dimensional graphene structure is a plurality of graphene
flowers wherein each graphene flower comprises a plurality of
voids.
5. The inorganic-organic hybrid material of claim 4 wherein the
three-dimensional structure is formed by: dispersing a graphene
precursor on a sacrificial support to produce a hybrid material;
atomizing the hybrid material; flowing the atomized hybrid material
through a pre-heated furnace to produce supported graphene
materials; collecting the supported graphene materials; heat
treating the collected supporting materials; and removing the
sacrificial support to produce voids.
6. The inorganic-organic hybrid material of claim 1 wherein the
three-dimensional graphene material, comprises graphene walls and
voids.
7. The inorganic-organic hybrid material of claim 6 wherein the
voids are formed by the removal of a sacrificial support
material.
8. The inorganic-organic hybrid material of claim 1 comprising a
plurality of voids that have been formed by the removal of a
sacrificial support material.
9. The inorganic-organic hybrid material of claim 1 wherein the
three-dimensional shape is a sphere or near-sphere.
10. The inorganic-organic hybrid material of claim 9 wherein the
sphere or near-sphere is formed by spray-pyrolysis.
11. The inorganic-organic hybrid material of claim 1 wherein the
predetermined structure comprises pores of a predetermined shape or
size.
12. The inorganic-organic hybrid material of claim 1, wherein the
graphene comprises between 3 and 20 layers of carbon atoms.
Description
BACKGROUND
Many compounds that are important for biology and medicine are
chiral, i.e. they have structural asymmetry and demonstrate optical
activity (rotation of polarization plane of propagating
electromagnetic radiation). For example, about 40% of
pharmaceutical drugs are chiral compounds, and only approximately
25% are used in the form of pure enantiomers. Quite frequently,
pharmacological efficiency is restricted to only one of the
enantiomers (eutomer), and in some cases the "mirror images" of
efficient drugs (distomers) demonstrate toxicity or undesirable
medical side effects. Furthermore, even if the distomers are
non-toxic, they have to be metabolized by the patient, which
represents an unnecessary burden to patient's metabolic system.
Therefore, the availability of chirally pure drugs is one of the
most important problems of modern pharmaceutics.
Ideally, the best solution to the problem would be direct
enantioselective synthesis of chiral drugs. Unfortunately, in many
cases this approach is very expensive, and, in a majority of cases,
impossible. Usually, synthesis provides racemic mixtures of
compound, containing an approximately 50:50% mixture of both
enantiomeric forms. Therefore, the separation of enantiomers is the
most realistic solution of the problem.
The issue of chiral separation is very important not only for the
pharmaceutical industry, but also as an analytical tool for
controlling the efficiency of synthesis and the quality/properties
of the synthesized products, monitoring the racemization processes,
investigation of pharmacokinetics, and other applications. Typical
methods of chiral separation include functional crystallization and
formation of diastereometric pairs followed by recrystallization.
In some cases separation procedures may include the use of enzymes.
Recently, capillary electrophoresis and chromatographic techniques
(and high performance liquid chromatography (HPLC) in particular)
became to be more and more popular method of chiral separation.
See, e.g., L. A. Nguyen, H. He, Ch. Pham-Huy, Chiral Drugs: An
Overview, International Journal of Biomedical science, 2(2) 85-100,
2006; W. H. Porter, Resolution of chiral drugs, Pure & Appl.
Chem., Vol. 63, No. 8, pp. 11 19-1 122, 1991; Chiral Separation
Techniques, A Practical Approach, 3.sup.rd edition, Ed. By G.
Subramanian, Wiley-VCH, 2007; Chiral Separations: Methods and
Protocols, Ed. By G. Gubitz and M. G. Schmid, Humana Press, 2004;
and Chromatographic Chiral Separations, Ed. By M. Zief and L. J.
Grane, Marcel Dekker, 1988.
However, each of these methods comes with its own drawbacks and
burdens including difficulty and expense. Accordingly, novel
methods and materials for chiral separations are desperately
needed.
SUMMARY
The present disclosure provides a variety of inorganic-organic
hybrid materials and methods for using the same. According to a
general embodiment, the hybrid materials are graphene or graphitic
materials populated with organic molecules. According to a further
embodiment, the hybrid materials have a variety of surface defects,
pits or three-dimensional architecture that increases the surface
area of the material. According to a still further embodiment, the
hybrid materials include three dimensional graphene nanosheets (3D
GNS) that take the form of non-contiguous graphene mono or
multi-layers comprising a plurality of defects and pores.
Alternatively, the 3D GNS may be thought of as disordered graphene
mono or multi-layered walls surrounding pores formed from the
removal of a plurality of sacrificial particles. According to a
still further embodiment the organic molecules are enantiospecific
molecules that enable the hybrid materials to be used for chiral
separation of racemic mixtures. Accordingly, the present disclosure
further provides methods for chiral separation of racemic mixtures
using the inorganic-organic hybrid materials disclosed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of the steps of a method for
producing 3D graphene structures according to an embodiment of the
present disclosure.
FIG. 2 is a schematic illustration of the steps of a spray
pyrolysis-based method for producing 3D graphene flowers according
to an embodiment of the present disclosure.
FIG. 3 is an illustration of the morphology of 3D graphene flowers
that can be produced using the methods disclosed in the present
disclosure.
FIG. 4 is a schematic illustration of the steps for chiral
separation of enantiomer according to an embodiment of the present
disclosure.
DETAILED DESCRIPTION
According to an embodiment the present disclosure provides novel
graphene-based inorganic-organic hybrid materials useful for a
variety of applications including, but not limited to, detection
and separation techniques, catalysis, concentration of diluted
solutions, desalination, wastewater treatment, gas adsorption etc.
According to a specific embodiment, these hybrid materials can be
used as the stationary phase for HPLC-based chiral separation of
chemical compounds.
In general, the hybrid materials of the present disclosure are
formed by chemically modifying the surface of graphene or graphitic
materials with organic molecules. According to an embodiment, the
hybrid materials have a variety of surface defects, pits or
three-dimensional architecture that increases the surface area of
the material. According to a further embodiment, the hybrid
materials include three dimensional graphene nanosheets (3D GNS)
that take the form of non-contiguous graphene mono or multi-layers
incorporating numerous defects and pores. According to a still
further embodiment the organic molecules are enantiospecific
molecules that enable the hybrid materials to be used for chiral
separation of racemic mixtures.
For the purposes of the present disclosure the term "mono-layer
graphene" refers to a flat, 2-dimensional sheet, or platelet,
formed from a single layer of carbon atoms arranged in a hexagonal
pattern. A graphene "multi-stack" or "few-layer graphene" is formed
from multiple individual layers of graphene sheets stacked on top
of each other. As an analogy, a graphene mono-layer might be
thought of as a sheet of paper, a graphene "multi-stack" (or
few-layer graphene) as several sheets of paper stacked on top of
each other. For the purposes of the present disclosure, anything
with a thickness of greater than 50 graphene layers will be
considered graphite, while 50 or fewer graphene layers is
considered graphene. Accordingly, graphene structures may have a
thickness of 50 or fewer layers, 20 or fewer layers, 10 of fewer
layers, 6 or fewer layers, 3 or fewer layers, 2 or fewer layers, or
only 1 layer of graphene.
Accordingly, while a three-dimensional graphene-like structure may
be formed by manipulating a single contiguous sheet or multiple
layers of contiguous sheets of graphene in the same way a sheet or
a few layered sheets of paper can be crumpled, folded, bent, or
otherwise manipulated to form a three-dimensional structure, the
present disclosure also contemplates non-contiguous three
dimensional graphene structures having one or more voids that are
defined and separated by graphene walls and wherein the walls of
the structures are formed from fewer than 50 layers of graphene. It
is important to note that, in this embodiment, the walls and
overall structure are not formed from a manipulated pre-formed
single contiguous sheet (or stack of sheets), and, in fact, in
"non-contiguous" embodiments, the overall structure could not be
"unrolled," or "uncrumpled," in order to form a single contiguous
sheet (as distinguished from, for example, carbon nanotubes, which
if unrolled, would form a single contiguous sheet).
For the purposes of the present disclosure a "graphene wall" is a
section of hexagonally arranged carbon atoms that forms the
physical structure of the final non-contiguous material. According
to some embodiments the graphene wall may consist of a single-layer
of hexagonally arranged carbon atoms or fewer than 3, fewer than 6,
fewer than 10, fewer than 20 or fewer than 50 layers of
single-layer sheets. As explained in more detail below, some or all
of the graphene walls in a particular embodiment may be more
"string-like" in appearance. However, unlike the graphene sheets
that have been previously described, which are simply flat
platelets, some or all of the graphene sheets or walls (and/or
portions thereof) formed by the methods described herein may be
curved, rounded, or otherwise non-planar in shape. Furthermore,
various walls may branch or connect with other walls to form the
complex 3D morphology described herein. Accordingly, it will be
understood that while the wall in general may be referred to as
having a specific thickness (i.e., 1, 5, or 10 layers of graphene
sheets) some or all of the wall junctions i.e., regions where one
or more "walls" connect, may be viewed as having a greater
thickness, even though the general structure is considered to have
an overall wall thickness of the 1, 5, or 10 layers, based on the
thinnest section of the wall.) Accordingly, for the purposes of the
present disclosure, the thickness of a particular graphene wall is
determined by the area in which the least number of carbon atoms
can be measured, (i.e., the thinnest portion of the wall).
According to some preferred embodiments, the graphene walls may
have a thickness of between 6 and 10 graphene layers. It will be
understood that while no particular wall will have a thickness of
more than 50 layers, because the structure may contain many walls
and many voids, the overall structure itself may have a much, much
larger diameter.
According to an embodiment, the 3D-GNS of the present disclosure
are produced using a sacrificial support-based method wherein one
or more graphene precursors, such as graphene oxide, or other
carbons are mixed with sacrificial particles. The
precursor/sacrificial support mixture is then reduced to produce a
hybrid graphene nanosheets that incorporates the sacrificial
particles as distinct elements within the nanosheets. The
sacrificial particles are then removed, resulting in a
"three-dimensional" graphene nanosheet incorporating a variety of
defects and pores (or voids) resulting from the removal of the
sacrificial particles. See e.g., the first three steps of the
exemplary synthesis route shown in FIG. 1. While it will be
understood from further reading that the methods described herein
enable the production of pores of virtually any size, shape,
diameter, and density, according to various specific embodiments,
the pores in question may have an average pore diameter of between
5 and 250 nm.
For the purposes of the present disclosure, the term "sacrificial
particle" is intended to refer to a particulate material that is
mixed with the graphene oxide and included during the graphene
nanosheet synthesis process in order to provide temporary structure
but which is mostly or entirely removed from the final product.
According to a specific embodiment, graphene oxide is produced
using a modified Hummers method (see e.g., W. S. Hummers, R. E.
Offeman, J. Am. Chem. Soc., 1958, 80, 1339). In general, graphite
flakes are added to sulfuric acid (H.sub.2SO.sub.4) and potassium
permanganate (KMnO.sub.4) solution under continuous stirring over a
heated water bath, followed by a slow addition of H.sub.2O.sub.2
(30%) to yield graphene oxide (GOx).
According to various embodiments of the present disclosure, the
graphene oxide and sacrificial particles are mixed under suitable
conditions. For example, the graphene oxide and sacrificial
particles may be mixed in solution and/or using the
mechano-chemical synthesis means as described below, in order to
coat, deposit, impregnate, infuse, or similarly associate the
graphene oxide with the sacrificial support. For the sake of
simplicity, unless otherwise specified, the term "coat" is used
herein as a catchall phrase to refer to any type of physical
association, whether or not the "coating" is complete or partial
and whether exclusively external or both internal and external. The
graphene/sacrificial particle mixture is dried, if necessary, and
reduced (for example via thermal or chemical reduction), and the
sacrificial support removed, resulting in a porous, irregularly
shaped, three-dimensional graphene nanosheet. It will be understood
that in contrast synthesis mechanisms that rely on templating to
reproduce the very specific, typically organized, structure of a
monolithic block template, the sacrificial support method of the
present disclosure results in a disorganized final structure that
is determined by the random placement of the sacrificial support
particles in the graphene precursor/sacrificial support
mixture.
According to some embodiments, the graphene precursor(s) and
sacrificial support particles may be mixed together under aqueous
conditions using known solvents such as water, alcohols, or the
like and using various known mechanical mixing or stirring means
under suitable temperature, atmospheric, or other conditions as
needed in order to enable or produce the desired degree of
dispersion of sacrificial particles within the mixture. It should
be understood that because the final morphology of the 3D-GNS
material is determined by the size, shape, and relative placement
of the sacrificial particles within the mixture, different
applications may require or benefit from different ratios or
degrees of dispersion of the particles within the graphene
oxide-sacrificial particle mixture. For example, clumping of the
particles (i.e. less even dispersion) with in the mixture could
result in larger pores and a higher degree of irregularity, which
could be desirable for some applications, which more evenly
dispersed particles could result in a more even distribution of
pores and more consistent pore sizes, which could be desirable in
other applications. Suitable mixing means include, for example, use
of an ultrasound bath, which also enables dispersion of the
sacrificial support particles.
Alternatively or additionally, the graphene precursor(s) and
sacrificial particles may be mixed together using mechano-chemical
synthesis techniques such as high energy ultrasonic power or
ball-milling.
It will be appreciated that the presently disclosed methods enable
the production of graphene nanosheets having highly predictable
morphology. Specifically, by selecting the ratio of sacrificial
support particles to graphene oxide and the size, shape, and even
porosity of the sacrificial template particles, it is possible to
control, select, and fine-tune the internal structure of the
resulting 3D graphene nanosheet material. In essence, the disclosed
method enables the production of 3D nanosheet having as convoluted
and tortuous a morphology as desired. For example, a highly porous
open-structure "sponge-like" material may be formed by using larger
sacrificial template particles, while a highly convoluted, complex
internal structure may be formed by using smaller, more complexly
shaped, sacrificial particles, including for example, sacrificial
particles of different shapes and/or sacrificial particles which
are themselves porous. Moreover, the "density" of the 3D material
can be selected by altering, for example, the ratio of sacrificial
particles to graphene precursor materials, the shape of the
template particles (i.e. how easily they fit together), or other
factors. Thus, it should be appreciated that while the overall
final structure of the material is disorganized and unpredictable,
various aspects of the structure, such as the density, pore size,
degree of porosity, and the like can be specifically
controlled.
Accordingly, it will be appreciated that the size and shape of the
sacrificial particles may be selected according to the desired
shape(s) and size(s) of the voids within the final product.
Specifically, it will be understood that by selecting the
particular size and shape of the support particles, one can produce
a material having voids of a predictable size and shape. For
example, if the template particles are spheres, the 3D material
will contain a plurality of spherical voids having the same general
size as the spherical particles.
As a specific example, assuming there is no alteration in the size
of the particle caused by the synthesis method, in an embodiment
where particles having an average diameter of 20 nm is used, the
spherical voids in the final product will typically have an average
diameter of approximately 20 nm. (Those of skill in the art will
understand that if the diameter of the particle is 20 nm, the
internal diameter of the void in which the particle resided will
likely be just slightly larger than 20 nm and thus the term
"approximately" is used to account for this slight adjustment.)
Accordingly it will be understood that the sacrificial particles
may take the form of any two- or three-dimensional regular,
irregular, or amorphous shape or shapes, including, but not limited
to, spheres, cubes, cylinders, cones, etc. Furthermore, the
particles may be monodisperse, or irregularly sized.
It will be further understood that because the material is formed
using a sacrificial support technique, where the sacrificial
material can be, for example, "melted" out of the supporting
materials using acid etching or other techniques, the resulting
material can be designed to have a variety of variously shaped
internal voids which result in an extremely high internal surface
area that can be easily accessed by, for example, gasses or liquids
that are exposed to material (for example, in a fuel cell).
Furthermore, because the size and shape of the voids is created by
the size and shape of the sacrificial particles, materials having
irregular and non-uniform voids can easily be obtained, simply by
using differently shaped sacrificial particles and/or by the
non-uniform distribution of sacrificial materials within the
graphene precursor/sacrificial particle mixture. Furthermore, the
sacrificial-support based methods of the present disclosure may
produce catalysts having, for example, a bi-modal (or even
multi-modal) pore distribution either due to the use of differently
sized sacrificial particles or where a first smaller pore size is
the result of removal of individual particles and thus determined
by the size of the sacrificial particles themselves and a second,
larger, pore size is the result of removal of agglomerated or
aggregated particles. Accordingly, it will be understood that the
method described herein inherently produces a material having a
unique morphology that would be difficult, if not impossible, to
replicate using any other technique.
As stated above, according to various embodiments, sacrificial
particles of any size or diameter may be used. In some preferred
embodiments, sacrificial particles having a characteristic
length/diameter/or other dimension of between 1 nm and 100 nm may
be used, in more preferred embodiments, sacrificial particles
having characteristic length/diameter/or other dimension of between
100 nm and 1000 nm may be used and in other preferred embodiments,
sacrificial particles having characteristic length/diameter/or
other dimension of between 1 mm and 10 mm may be used. It should
also be understood that the term "sacrificial particle" is used
herein as a term of convenience and that no specific shape or size
range is inherently implied by the term "particle" in this context.
Thus while the sacrificial particles may be within the nanometers
sized range, the use of larger or smaller particles is also
contemplated by the present disclosure.
According to some embodiments, the sacrificial particles may
themselves be porous. Such pores may be regularly or irregularly
sized and/or shaped. The use of porous sacrificial particles
enables the graphene precursor(s) to intercalate the pores,
producing even more complexity in the overall three-dimensional
structure of the resulting catalyst.
It will be appreciated that the sacrificial particles may be
synthesized and mixed (or coated, or infused, etc.) in a single
synthesis step or the graphene precursor(s) may be mixed with
pre-synthesized (whether commercially purchased or previously
synthesized) sacrificial particles.
Of course it will be appreciated that given the various conditions
that the sacrificial template will be subjected to during the
synthesis process, it is important to select a sacrificial material
which is non-reactive to the catalytic materials under the specific
synthesis conditions used and the removal of which will not damage
the final material. For example, if the supporting material is to
be used as an active support (i.e. a support which can
synergistically promote the main catalyst), it is important that
the method(s) used to remove the sacrificial particles not damage
the support's active sites.
Silica is a material known to easily withstand the conditions
described herein while remaining inert to a variety of catalytic
materials including the metals described herein. Furthermore,
silica can be removed using techniques that are harmless to
graphene materials. Thus, silica is considered to be a suitable
material from which the sacrificial template particles can be made.
According to some specific embodiments, 20 nm diameter spheres
formed from mesoporous silica can be used. In this case the
templating involves intercalating the mesopores of the silica
template particles and the resulting material typically contains
pores in the 2-20 nm range. In one particular embodiment, the
silica template is commercially available Cabosil amorphous silica
(400 m.sup.2/g.sup.-1). Furthermore, selecting a different type of
silica can also alter the shape and size of the pores in the final
3D-GNS product. Those of skill in the art will be familiar with a
variety of silica particles that are commercially available, and
such particles may be used. Alternatively, known methods of forming
silica particles may be employed in order to obtain particles of
the desired shape and/or size.
However, while many of the examples herein utilize silica for the
templating materials, it will be appreciated that other suitable
materials may be used including, but are not limited to, zeolites,
aluminas, clays, magnesia and the like.
As stated above, after the graphene precursor is mixed with the
sacrificial support, the mixture is reduced to produce a hybrid
graphene nanosheet that incorporates the sacrificial particles as
distinct elements within the nanosheet. According to some
embodiments, the hybrid material may be thermally reduced.
Reduction may be performed, for example in hydrogen gas at a
temperature of between 250 and 1200 K for between 30 and 240
minutes.
After reduction, the hybrid GNS-sacrificial particle material can
be ball-milled or subjected to high energy ultrasonic power to
re-disperse and thus form a more uniform powder, if desired.
The sacrificial particles are then removed resulting in an
amorphous, porous, 3D nanosheet. Removal of the sacrificial
template particles may be achieved using any suitable means. For
example, the template particles may be removed via chemical
etching. Examples of suitable etchants include NaOH, KOH, and HF.
According to some embodiments, HF may be preferred as it is very
aggressive and can be used to remove some poisonous species from
the surface of the material. Accordingly, those of skill in the art
will be able to select the desired etchants based on the particular
requirements of the supporting material being formed.
As a specific example, 3D-GNS materials were formed using the
Sacrificial Support Method described above. A calculated amount of
graphene oxide (2 g) was fully exfoliated in 100 ml of water using
a high energy ultrasonic probe (the amount of energy delivered was
600 kJ). In a separate beaker, 5 g of silica (with a surface area
400 m.sup.2 g.sup.-1) was dispersed in 50 ml of water using an
ultrasonic bath. The two colloidal solutions were then mixed
together and ultrasonicated for 2 h in an ultrasonic bath. The
water was evaporated at T=85 C for 12 h. The resulting solid hybrid
GO/SiO.sub.2 material was ball-milled at 400 RPM for 30 m. A final
reduction of graphene oxide to GNS was performed at T=800 C, t=1 h
in atmosphere of 7 at % of H.sub.2. The silica was then removed by
leaching with 25 wt % of HF overnight, the powder was then washed
with DI water until neutral pH was achieved and dried at T=85 C
overnight.
According to some embodiments it may be desirable to produce 3D-GNS
materials that are spherical or nearly-spherical in shape. For
example, as mentioned above, the hybrid materials of the presently
disclosure may be used as the stationary phase for HPLC-based
chiral separations. However, it will be understood that in some
HPLC systems, it is desirable or typical that the stationary phase
take the form of packed spheres (or "near-spheres"). Accordingly
the present disclosure provides a method for forming 3D-GNS
sphere-like shapes. As shown in FIG. 2, the 3D-GNS structures of
the present disclosure can be formed by a combination of spray
pyrolysis and the sacrificial template method described above. In
this embodiment, graphene precursor(s) such as graphene oxide is
dispersed on a sacrificial support as described above with respect
to the sacrificial support method, the hybrid material is then
atomized, for example, by use of an ultra-high power ultrasonic
probe, and then transported by flowing inert/reactive/reductive gas
through a pre-heated furnace. The supported graphene materials are
then collected on a filter and heat treated. After heat treatment,
the sacrificial support is removed, using the techniques described
above.
The combined spray pyrolysis/sacrificial support method offers a
fast and cost-effective method for producing large amounts of 3D
graphene materials. FIG. 3 is a schematic illustration of the types
of structures, referred to as "graphene flowers" that can be
produced using this technique.
While much of the present disclosure is directed to the use of
non-contiguous 3D GNS, it should be understood that the present
disclosure contemplates a variety of different types of carbon and
graphitic materials that could be modified using the methods
described herein used for a variety of applications including, for
example, the chiral separation applications described in greater
detail below. Suitable types of carbon, graphene, and graphitic
materials include, but are not limited to 3D GNS, 2D GNS, pristine
graphite, carbon nanotubes, fullerenes, etc.
2D GNS can be prepared using know methods including, for example,
chemical vapor deposition. Alternatively, 2D GNS can be prepared by
chemical or thermal reduction of graphene oxide. For example,
according to a specific embodiment, 5 g of GO.sub.x was dispersed
in 100 ml of DI H.sub.2O by ultrasonic treatment with high energy
probe. The resulting solution was heated to 85.degree. C. and 150
ml of hydrazine hydrate (20 wt %) was added while stiffing on a
magnetic stirrer. After 30 minutes, the color of the solution
changed from brown to black and coarse particles of reduced
graphene oxide precipitated. The resulting powder was filtrated,
washed, and dried.
It should be understood that the 2D GNS or other types of graphitic
materials can be altered to include defects, pits, and/or other
malformations to increase surface area. For example, according to
another embodiment, pristine graphite was ball-milled at 400 RPM
for 2 hours resulting in formation of highly defective structure
with medium surface are of 20 m.sup.2g.sup.-1.
As stated above, according to some embodiments, the graphene and or
graphitic materials described above undergo covalent modification
and attachment of a functional group.
The 2D/3D GNS or graphite-like materials described herein can be
functionalized using any suitable procedure including, but not
limited to, different types of cycloaddition, radical addition,
functionalization using diazonium salts, organometallic
functionalization, etc. It will be understood that the specific
organic molecule bound to the 2D/3D GNS or graphite-like materials
will be determined by the desired use for the material and
therefore, the specific mechanism for attaching the organic
molecule to the 2D/3D GNS or graphite-like materials will be
determined by the attachment mechanisms that are available and/or
necessitated by the structure and properties of the organic
molecule and the material to which it will be attached.
According to an embodiment, 2D/3D GNS or graphite-like materials is
modified with tetracyanoethylene oxide (TCNEO). In an example of an
embodiment utilizing 3D-GNS, the 3D-GNS is heated with TCNEO for an
appropriate amount of time (e.g., 48 hours) in chlorobenzene at a
suitable temperature (e.g., 150-160.degree. C.). It is noted that
this is the first time chlorobenzene was used as a solvent and that
this reaction time is significantly longer than previously
described methodologies. The functionalized 3D-GNS is then removed
and washed by different organic solvents, for example methanol,
acetone, acetonitrile and others. Additional information regarding
the modification of graphite or graphene materials with TCNEO may
be found in L. V. Frolova, I. V. Magedov, A. Harper, S. K. Jha, M.
Ovezmyradov, G. Chandler, J. Garcia, D. Bethke, E. A. Shaner, I.
Vasiliev, N. G. Kalugin, Tetracyanoethylene oxide-functionalized
graphene and graphite characterized by Raman and Auger
spectroscopy, Carbon 81, January 2015, Pages 216-222, which is
hereby incorporated by reference.
The functional groups attached to the 2D, 3D GNS or graphite-like
materials can then act as enantiomer separators themselves or as
anchors for an appropriate organic molecule. According to an
embodiment, hydrolysis or reduction on the functionalized 2D, 3D
GNS or graphite-like materials can be performed and then a desired
organic molecule is bound for example, by ester bonding or amide
bonding.
According to various embodiments, the hybrid materials can the be
used in various experiments including, but not necessarily limited
to, those wherein the bound molecule selectively binds to a target
molecule in a sample, making the hybrid material useful for a wide
variety of separation and/or detection techniques. As stated above,
according to a specific example, the bound molecule may selectively
bind to one enantiomer of a chemical compound. For example, the
hybrid materials of the present disclosure can easily be used as
the stationary phase in HPLC-based chiral separations. A schematic
of HPLC-based chiral separations is shown in FIG. 4. Briefly, an
enantioselective molecule is bound to a hybrid material as
described above. The enantiomers are then separated by flowing a
racemic mixture through a chromatographic column. The presence of
the enantioselective molecule on the hybrid material causes the
different enantiomers to travel at different rates through the
column, such that the first enantiomer exits the column ahead of
the second enantiomer.
As a specific example, a hybrid 3D-GNS material as described above
has been used for separation of ibuprofen enantiomers in racemic
solutions. Ibuprofen is an optically active compound with both S-
and R-isomers, with the S-isomer being more biologically active. In
this particular example, the 3D-GNS was modified with TCNEO as
described above. The TCNEO-modified hybrid material was then
hydrolyzed and (S)-(+)-2-pyrrolidinemethanol attached via
esterification (in this case (S)-(+)-2-pyrrolidinemethanol plays a
role of enantiomer separator). In general, hydrolysis of the TCNEO
cyanogroups can be performed by heating the modified material in
acid and then washing in a base until neutral pH is achieved,
followed by a second washing step and etherification. According to
a specific example, 200 mg of modified material was heated in 7 ml
of H.sub.2SO.sub.4/H.sub.2O (2/1 mixture) for 24 hours. The
material was then filtered out and washed with H.sub.2O and
KHCO.sub.3 until reaching pH7. The material was subsequently washed
with methanol, acetone, and acetonitrile and dried overnight.
Etherification was performed by treating 200 mg of the hydrolyzed
material with (S)-(+)-2-pyrrolidinemethanol in the presence of DMAP
and DCC in dry methylene chloride under nitrogen for 3 days.
Finally, the 3D-GNS hybrid was filtered, and washed with solutions
of KHCO.sub.3 and HCl, deionized H2O, methanol, acetone and
acetonitrile. The proline-modified 3D-GNS material was then used as
the substrate in a separation column and, separation of the R and S
isomers was achieved, as confirmed by polarimetry measurements.
Examples of suitable racemic mixtures that would benefit from the
type of enantiomeric separation described herein includes, but is
not limited to, racemic mixes of organic acids (racemic mixture A),
racemic mixture of organic bases, racemic mixtures of lipophilic
molecules, racemic mixtures of lipophobic compounds which can be
separated by hybrid material having enantiomer pure molecules
attached as the enantiomer separators--
One of the advantages of the presently described system, is that
the morphology of the 3D GNS hybrid can easily be modified as
described above (for example, to increase or decrease surface area,
porosity, tortuousness, etc.) so as to increase or decrease the
density of the bound organic molecules, providing a mechanism for
fine-tuning of the interactions between a target molecule and the
bound molecule.
Furthermore, with regard to its ability to separate racemic
mixtures, the 3D GNS material described herein has a very high
capacity, our experiments demonstrated that 200 mg of modified
material was able to separate 10 mg of racemic mixture of
ibuprofen. Moreover, the hybrid material is highly durable allowing
the use of a wide variety of solvents that are not available for
use with currently existing commercially available racemic mixture
separation preparations. These solvents include, but are not
limited to, methylene chloride, methanol, and acetonitrile.
The terms and expressions that have been employed are used as terms
of description and not of limitation, and there is no intent in the
use of such terms and expressions to exclude any equivalent of the
features shown and described or portions thereof, but it is
recognized that various modifications are possible within the scope
of the invention as claimed. Thus, it will be understood that
although the present invention has been specifically disclosed by
preferred embodiments and optional features, modification and
variation of the concepts herein disclosed may be resorted to by
those skilled in the art, and that such modifications and
variations are considered to be within the scope of this invention
as defined by the appended claims.
All patents and publications mentioned herein are indicative of the
levels of skill of those skilled in the art to which the invention
pertains, and each such referenced patent or publication is hereby
incorporated by reference to the same extent as if it had been
incorporated by reference in its entirety individually or set forth
herein in its entirety. Applicants reserve the right to physically
incorporate into this specification any and all materials and
information from any such cited patents or publications.
* * * * *